Abstract
Detailed measurements of the atmospheric turbulence and climatological conditions have been carried out at the site of the Observatorio Astronómico Nacional at San Pedro Mártir. The results obtained during a three year period with the Site Testing Telescope from Steward Observatory yielded a median seeing of 0.61 arcsec and a first quartile of 0.50 arcsec. These were confirmed by independent and simultaneous measurements with the monitor of the Observatories of the Carnegie Institution. We detect a seasonal dependence on the seeing, with better results during spring and summer when we find a median of 0.59 arcsec, compared with autumn and winter, which have a median of 0.69 arcsec. Measurements with the Micro-Thermal Array show that the seeing decreases by 0.1 arcsec at a height of 15 meters. The seeing does not seem to depend strongly on meteorological variables like wind direction and velocity, humidity or external temperature.
